The Cannabis Breeder's Bible (6 page)

MAKING A SIMPLE HYBRID

Again, making a simple hybrid is easy. Just take a male plant from one strain and a female plant from another, for example Big Bud and Skunk. The result will be Big Bud x Skunk, but there will be differences in the offspring. Some of the plants will exhibit more Big Bud traits and some will exhibit more Skunk traits. Genes not expressed by each of the parents may also appear in the offspring.

If you want to breed for specific traits by eliminating variations, ultimately creating uniform plants or even an IBL, then you should start with a basic knowledge of plant genetics.

INTRODUCTION TO PLANT GENETICS

Genetics can be somewhat difficult to understand at first so we’ll start by explaining a few rudimentary concepts and the basic terminology. The explanations for the words below can be treated as a glossary for your benefit.

Genes

Genes are the units of heredity transmitted from parent to offspring, usually as part of a chromosome. Genes usually control or determine a single characteristic in the offspring. There are genes responsible for each feature of your plant to be inherited, including leaf color, stem structure, texture, smell, potency, etc.

Gene Pairs

All of life is made up of a pattern of genes. You can think of this pattern as being similar to the two sides of a zipper. One side is inherited from the mother and the other from the father. Each gene occupies a specific locus, or particular space on the chain, and controls information about the eventual characteristics of the plant. So each gene locus contains two genes, one from the mother and one from the father. These gene pairs are usually denoted by a pair of letters, such as BB, Bb, Pp, pp, etc. Capital letters refer to dominant genes while lowercase letters refer to recessive genes. By way of example, B can represent Big Bud while b can represent small bud. Any letter can be assigned to any trait or gene pair when you are working out your own breeding program.

HYBRIDIZING FOR SELECTION

Hybridizing through multiple selections for better selections.

Chromosome

A threadlike structure of nucleic acids and proteins in the cell nuclei of higher organisms that carries a set of linked genes, usually paired.

Locus

A position on a chromosome where a particular gene pair is located.

Allele

Alleles are any of a number of alternative forms of one gene. For example the gene for purple bud color may have two forms, or alleles, one for purple and one for dark red.

Homozygous

Having identical alleles at one or more genetic loci, which is not a heterozygote (see below) and breeds true. Your plant is said to be homozygous for one feature when it carries the same gene twice in the responsible gene pair, which means both genes of the gene pair are identical.

Heterozygous

Having different alleles at one or more genetic loci. Your plant is said to be heterozygous for one feature when the genes of the responsible gene pair are unequal, or dissimilar.

Phenotype

The phenotype is the summary of all of the features you can detect or recognize on the outside of your plant, including color, smell and taste.

Genotype

The
genotype
is the genetic constitution of your plant, as distinguished from the phenotype. The genotype characterizes how your plant looks from the inside. It is the summary of all the genetic information that your plant carries and passes on to its offspring.

Dominant

Dominant is used to describe a gene or allele that is expressed even when inherited from only one parent. It is also used to describe a hereditary trait controlled by a gene and appearing in an individual to the exclusion of its counterpart, when alleles for both are present. Only one dominant allele in the gene pair must be present to become the expressed genotype and eventually the expressed phenotype of your plant.

Recessive

Recessive describes a gene, allele or hereditary trait perceptibly expressed only in homozygotes, being masked in heterozygotes by a dominant allele or trait. A gene is called recessive when its effect cannot be seen in the phenotype of your plant when only one allele is present. The same allele must be present twice in the gene pair in order for you to see it expressed in the phenotype of your plant.

BACKCROSSING

The backcross breeding method.

Dominant/Recessive and Genetic Notation

Assume that the dominant ‘B’ allele carries the hereditary trait for Big Bud, while the recessive ‘b’ allele carries the hereditary trait for small bud. Since B is dominant, a plant with a Bb genotype will always produce Big Bud. The B is dominant over the b. In order for a recessive gene to be displayed in the phenotype, both genes in the gene pair must be recessive. So a plant with the BB or Bb gene will always produce Big Bud. Only a plant with the bb gene will produce small bud.

Now that we have explained the basic terminology of plant genetics, we can move on to the next step: rudimentary breeding concepts as laid out in the Hardy-Weinberg law of genetic equilibrium.

THE HARDY-WEINBERG MODEL OF GENETIC EQUILIBRIUM

An understanding of plant breeding requires a basic understanding of the Hardy-Weinberg law. To illustrate the value of the Hardy-Weinberg law, ask yourself a question, like: “If purple bud color is a dominant trait, why do some of the offspring of my purple bud strain have green buds?” or “I have been selecting Indica mothers and cross-breeding them with Mostly Indica male plants but I have some Sativa leaves. Why?” These questions can be easily answered by developing an understanding of the Hardy-Weinberg law and the factors that can disrupt genetic equilibrium.

The first of these questions reflects a very common misconception: that the dominant allele of a trait will always have the highest frequency in a population and the recessive allele will always have the lowest frequency. This is not always the case. A dominant trait will not necessarily spread to a whole population, nor will a recessive trait always eventually die out.

Gene frequencies can occur in high or low ratios, regardless of how the allele is expressed. The allele can also change, depending on certain conditions. These changes in gene frequencies over time result in different plant characteristics.

A genetic population is basically a group of individuals of the same species (Cannabis Indica or Cannabis Sativa) or strain (Skunk#1 or Master Kush) in a given area whose members can breed with one another. This means that they must share a common group of genes. This common group of genes is locally known as the gene pool. The gene pool contains the alleles for all of the traits in the entire population. For a step in evolution—a new plant species, strain or trait—to occur, some of the gene frequencies must change. The gene frequency of an allele refers to the number of times an allele for a particular trait occurs compared to the total number of alleles for that trait in the population. Gene frequency is calculated by dividing the number of a specific type of allele by the total number of alleles in the gene pool.

Genetic Equilibrium Theory and Application

The Hardy-Weinberg model of genetic equilibrium describes a theoretical situation in which there is no change in the gene pool. At equilibrium there can be no change or evolution.

RANDOM MATING

Wild non-random mating resulting in unknown male donors.

Let’s consider a population whose gene pool contains the alleles B and b.

Assign the letter p to the frequency of the dominant allele B and the letter q to the frequency of the recessive allele b. We know that the sum of all the alleles must equal 100 percent, so:

p + q = 100%

This can also be expressed as:

p + q = 1

And all of the random possible combinations of the members of a population would equal:

p
²
+ 2pq + q
²

Where:

p = frequency of the dominant allele in a population
q = frequency of the recessive allele in a population
p
²
= percentage of homozygous dominant individuals
q
²
= percentage of heterozygous recessive individuals
2pq = percentage of heterozygous individuals

Imagine that you have grown a population of 1,000 ‘Black Domina’ cannabis plants from seeds obtained from a well-known seed bank. In that population, 360 plants emit a skunky smell, while the remaining 640 plants emit a fruity smell. You contact the seed bank and ask them which smell is dominant in this particular strain. Hypothetically, they tell you that the breeder selected for a fruity smell and the skunk smell is a recessive genotype. You can call this recessive genotype ‘vv’ and use the formula above to answer the following questions.

Question:
According to the Hardy-Weinberg law, what is the frequency of the ‘vv’ genotype?

Answer:
Since 360 out of the 1,000 plants have the ‘vv’ genotype, then 36% is the frequency of ‘vv’ in this population of ‘Black Domina.’

Question:
According to the Hardy-Weinberg law, what is the frequency of the ‘v’ allele?

WILD POLLINATION

Cannabis pollination and seed production.

Answer:
The frequency of the ‘vv’ allele is 36%. Since q
²
is the percentage of homozygous recessive individuals, and q is the frequency of the recessive allele in a population, the following must also be true: